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SecuritySecurity

PART PART VIIVII

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Security Topics

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Chapters

Chapter 29 Cryptography

Chapter 30 Message Authentication, User Authentication, and Key Management

Chapter 31 Security Protocols in The Internet

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Chapter 29

Cryptography

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29.1 Introduction29.1 Introduction

Introduction Introduction to to

CryptographyCryptography

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Figure 29.1 Cryptography components

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Figure 29.2 Encryption and decryption

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In cryptography, the encryption/decryption algorithms

are public; the keys are secret.

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29.2 Symmetric-Key Cryptography29.2 Symmetric-Key Cryptography

Traditional Cipher

Block Cipher

Operation Modes

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Figure 29.3 Symmetric-key cryptography

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In symmetric-key cryptography, the same key is used by the sender (for encryption) and the receiver (for decryption). The key is shared.

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In symmetric-key cryptography, the same key is used in both directions.

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Symmetric-key cryptography is often used for long messages.

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Figure 29.4 Caesar cipher

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Figure 29.5 Example of monoalphabetic substitution

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In monoalphabetic substitution, the relationship between a character in the

plaintext to the character in the ciphertext is always one-to-one.

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Figure 29.6 Vigenere cipher

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In polyalphabetic substitution, the relationship between a character in the

plaintext and a character in the ciphertext is one-to-many.

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Figure 29.7 Transpositional cipher

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Figure 29.8 Block cipher

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Figure 29.9 P-box

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Figure 29.10 S-box

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Figure 29.11 Product block

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Figure 29.12 DES

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Figure 29.13 General scheme of DES

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Figure 29.14 Iteration block

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Figure 29.15 Triple DES

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The DES cipher uses the same concept as the Caesar cipher, but the

encryption/decryption algorithm is much more complex due to the sixteen 48-bit keys derived from a 56-bit key.

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Figure 29.16 ECB mode

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Figure 29.17 CBC mode

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Figure 29.18 CFM

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Figure 29.19 CSM

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29.3 Public-Key Cryptography29.3 Public-Key Cryptography

RSA

Choosing Public and Private Keys

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Figure 29.20 Public-key cryptography

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Public-key algorithms are more efficient for short messages.

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Figure 29.21 RSA